offmap: introduce high-level setter for key/value pairs

Currently, there is only one caller that adds entries into an offset map, and
this caller first uses `git_offmap_put` to add a key and then set the value at
the returned index by using `git_offmap_set_value_at`. This is just too tighlty
coupled with implementation details of the map as it exposes the index of
inserted entries, which we really do not care about at all.

Introduce a new function `git_offmap_set`, which takes as parameters the map,
key and value and directly returns an error code. Convert the caller to make use
of it instead.

src/offmap.c

@@ -51,6 +51,24 @@ void *git_offmap_get(git_offmap *map, const git_off_t key)
 	return kh_val(map, idx);
 }
 
+int git_offmap_set(git_offmap *map, const git_off_t key, void *value)
+{
+	size_t idx;
+	int rval;
+
+	idx = kh_put(off, map, key, &rval);
+	if (rval < 0)
+		return -1;
+
+	if (rval == 0)
+		kh_key(map, idx) = key;
+
+	kh_val(map, idx) = value;
+
+	return 0;
+}
+
+
 size_t git_offmap_lookup_index(git_offmap *map, const git_off_t key)
 {
 	return kh_get(off, map, key);

src/offmap.h

@@ -61,6 +61,21 @@ size_t git_offmap_size(git_offmap *map);
  */
 void *git_offmap_get(git_offmap *map, const git_off_t key);
 
+/**
+ * Set the entry for key to value.
+ *
+ * If the map has no corresponding entry for the given key, a new
+ * entry will be created with the given value. If an entry exists
+ * already, its value will be updated to match the given value.
+ *
+ * @param map map to create new entry in
+ * @param key key to set
+ * @param value value to associate the key with; may be NULL
+ * @return zero if the key was successfully set, a negative error
+ *         code otherwise
+ */
+int git_offmap_set(git_offmap *map, const git_off_t key, void *value);
+
 size_t git_offmap_lookup_index(git_offmap *map, const git_off_t key);
 int git_offmap_valid_index(git_offmap *map, size_t idx);
 

src/pack.c

@@ -147,8 +147,7 @@ static int cache_add(
 		git_off_t offset)
 {
 	git_pack_cache_entry *entry;
-	int error, exists = 0;
-	size_t k;
+	int exists;
 
 	if (base->len > GIT_PACK_CACHE_SIZE_LIMIT)
 		return -1;
@@ -166,9 +165,7 @@ static int cache_add(
 			while (cache->memory_used + base->len > cache->memory_limit)
 				free_lowest_entry(cache);
 
-			k = git_offmap_put(cache->entries, offset, &error);
-			assert(error != 0);
-			git_offmap_set_value_at(cache->entries, k, entry);
+			git_offmap_set(cache->entries, offset, entry);
 			cache->memory_used += entry->raw.len;
 
 			*cached_out = entry;